Remember that corals and their zooxanthellae adapt to changes in their surroundings the same as we humans do. Whereas we may shade our eyes from bright sunlight, these animals have no such luxury. They must react as only they can, by recoil and a slow but gradual return to normal behavior. Interesting how we can't discuss lighting without getting involved in the coral's actual physical properties, isn't it? Well, after all it IS the primary reason for lighting at all!
About Lighting For SPS Corals
SPS (Short/Small Polyped Stony) corals are by far the most numerous in the skeleton category. I will not delve into the physiology or other biological factors of these corals, other than to state that they, above all others, require the most dynamic of light sources.
Not until the advent of aquarium related halide lamps was this light source truly ready for our use. The incredible intensity of the metal halide lamp makes providing the right output of light ideal for maintaining these delicate-to-establish corals. Once they grab hold, SPS corals can be the most prolific of all their kind, growing at enormous rates and prompting many cuttings. These coral cuttings, known as frags, can then be propagated through "coral-farming", which is highly practiced by many hobbyists and commerical aquaculturing companies today.
Naturally, factors other than the lights themselves contribute to the success of any coral, but once the water parameters and the lighting system are acceptable to the animals themselves, watch out. LOL!